As the image quality of digital color image forming apparatuses such as printers and copying machines has remarkably improved, high-quality full-color prints are easy to obtain. That is, anybody can obtain a desired print by image processing using a high-performance scanner, printer, copying machine, or computer. This also poses a problem of forgery of bills or securities, so some image processing apparatuses are equipped with a function of preventing forgery.
The forgery preventing function is generally comprised of two functions: a forgery tracking function and a forgery recognition function. The forgery tracking function embeds, e.g., a regular dot pattern representing an ID or model code unique to the printing apparatus in an image to be printed. If a forged bill is found, the IP or model code is extracted from the dot pattern embedded in the image of the forged bill, thereby specifying the printing apparatus used for forgery.
As is known, such a dot pattern is embedded in a printed image formed from, e.g., yellow, magenta, cyan, and black color components, using yellow with the lowest visibility.
If it is determined that a digital image to be printed coincides with or is similar to a bill image registered in the apparatus in advance, the bill recognition function stops outputting the digital image or deforms the output image to prevent faithful output of the digital image.
FIG. 1 shows an apparatus that can be specified by the forgery tracking function from a print that was distributed via a plurality of apparatuses. A copying machine with an ID CB, which has finally output the image of the forged print, can be specified. However, a copying machine having an ID CA, which has output the original used for copying by the copying machine with the ID CB, i.e., the image used as the original, or a scanner with an ID SA, which has been used to read the images of the bills or securities, cannot be specified. Printers except copying machines do not always have the forgery tracking function. Hence, for even a printer used to output a forged print cannot be specified.
When progress in recent computer networks represented by the Internet and image data communication thereon are taken into consideration, information such as the above ID or model code need be embedded in images as many as possible. Especially, it is more preferable to efficiently embed history information representing an apparatus via which image data was distributed on a network.